So, my boyfriend has officially gotten interested in fish now because of our guppies. He's curious about the following for our new 40 Breeder:

Non-aggressive

Active

Singular

Freshwater

Semi-tropical

I personally want shoaling or schooling, but if so they need to be distinguishable like guppies. He doesn't really like uniform with schools/shoals - wants to be able to tell this one from that one. And I don't care for angelfish that much, personally.

GOLDFISH! Lol! They do fit all of your requirements, and you could have 2-3 in that tank. Only thing is they like to be in groups instead of a single fish.

If you're looking for fish that are distinguishable you're really going to be looking for things like livebearers or other fish with captive bred morphs. You can get a couple different color varieties of platies or swordtails. Some livebearers you can't keep together, but I don't remember which ones. And most livebearers can be kept at cooler than tropical temperatures (below 75F).

Bringing back my thread... I meant semi aggressive in the first post there (I think), but oh well.

So. Boyfriend wants a semi aggressive tank for the 40. What if I did a sorority with about 6-8 (betta) girls and a ghost knife? The knife doesn't have very good eyesight and thus is rather unlikely to eat the girls.

Prolly a standing, in-tank filter on a ramp of sorts to create a small current, sparse plants if doing them (with MTS to stir the sand).

Reason I'm thinking 6-8 girls is because we got our (first) betta last night and there was a CT female, red/white that I found to be rather attractive. (And I'm addicted to fish and they would easily obtained, though expensive unless Petco offers discounts on "bulk" purchases.)

Definitely no girls in with the knife. They're pretty good at what they do despite bad eyesight and girls really don't move that fast[especially not when they're comfortable]. Past that, the knife will need atleast a 100+gal tank when it's full grown.

Ghost Knives don't get more than 10 inches. What I've read was that they need a minimum of about 50 but with enough filtration they could do a 40, especially with the width. Brown knives I would expect need a bit bigger than ghosts. /headtilt

Black Ghost Knifefish (Apteronotus albifrons) are most assuredly not suited for a tank of that size. They will grow to about a foot in captivity and have inflexible spines. They are a weakly electric fish (which is how they find prey) and produce electric currents using the muscles along the spine hence why it is inflexible. They need a tank that is at least double as wide as they are long to move around properly. A 40 is okay as a temporary grow-out, but is not suitable long-term. You are looking at a 100+ gal tank when it is fully grown.

As for the female bettas, they will become a midnight snack. BGK are very adept predators and do not use their eyes to hunt; they use electrical impulses and hunt at night when the bettas are sleeping.

If you are truly looking for a semi-aggressive community, look into cichlids. If you have soft water there are South American cichlids; for hard water there are the africans.

Ahhh, okay. I will definitely keep this in mind. I did let my boyfriend know so we definitely aren't getting a Knife. I'm trying to talk him into a sorority but it's not going so well... I know he's had his eye on some cichlids so we might go with them, but don't they get big? Or am I getting them mixed up with oscars? What about gouramis?